Lymphangioleiomyomatosis (LAM) is a multisystem disease affecting 30-40% of women with tuberous sclerosis complex (TSC), an often-fatal disease which is characterized by the widespread proliferation of abnormal smooth muscle-like cells that grow aberrantly in the lung. The proliferation of these cells (referred to as LAM cells) leads to the formation of cysts in the lungs and fluid-filled cystic structures in the axial lymphatics (referred to as lymphangioleiomyomas). The result is progressive cystic destruction of the lung parenchyma, obstruction of lymphatics, airways, and progressive respiratory failure. In addition, LAM cells can form tumors. These are generally slow growing hamartomas referred to as angiomyolipomas. Renal angiomyolipomas can lead to renal failure in LAM patients. The abnormal proliferation of LAM cells is caused at least in part by an inactivating mutation in one of the tuberous sclerosis complex tumor suppressor genes, TSC1 or TSC2. The TSC genes are negative regulators of the mammalian target of rapamycin (mTOR). The mTOR pathway is an important control point for cell growth, metabolism, and cell survival. As a consequence of the inactivation of TSC genes, LAM cells show constitutive activation of mTOR and many other kinases in the mTOR pathway including Akt, and S6K.
LAM generally occurs in women of child-bearing age although it may also occur in men. While it is most prevalent in women having TSC, it can also occur in persons who do not have clinical manifestations of TSC, as well as those who do not have germline mutations in the TSC1 or TSC2 tumor suppressor genes. These cases are referred to as sporadic LAM. Thus, LAM can occur as a sporadic, non-heritable form as well as in association with tuberous sclerosis complex.
Although LAM can progress slowly, it ultimately leads to respiratory failure and death. Ten years after the onset of symptoms 55% of patients are breathless, 20% are on oxygen and 10% are deceased. See e.g., Johnson et al. 2004 Thorax. Survival and disease progression in UK patients with lymphangioleiomyomatosis. There is no currently approved drug for the treatment or prophylaxis of LAM. The primary treatment options include the off-label use of oral rapamycin (sirolimus, which is FDA approved for the prophylaxis of organ rejection and renal transplantation, see below), or off-label use of oral everolimus.
Rapamycin is a macrocyclic triene antibiotic produced by Streptomyces hygroscopicus. See e.g., U.S. Pat. No. 3,929,992. Rapamycin is an inhibitor of mTOR. The immunosuppressive and anti-inflammatory properties of rapamycin initially indicated its use in the transplantation field and in the treatment of autoimmune diseases. For example, it was shown to prevent the formation of humoral (IgE-like) antibodies in response to an albumin allergic challenge, to inhibit murine T-cell activation, and to prolong survival time of organ grafts in histoincompatable rodents. In rodent models of autoimmune disease, it suppresses immune-mediated events associated with systemic lupus erythematosus, collagen-induced arthritis, autoimmune type I diabetes, autoimmune myocarditis, experimental allergic encephalomyelitis, graft-versus-host disease, and autoimmune uveoretinitis.
Rapamycin is also referred to by its generic drug name, sirolimus (see for example, ANDA #201578, by Dr. Reddys Labs Ltd., approved May 28, 2013). Sirolimus is FDA approved and marketed in the United States for the prophylaxis of organ rejection and renal transplantation under the trade name RAPAMUNE by Wyeth (Pfizer). It is in the form of an oral solution (1 mg/ml) or tablet (multiple strengths). Wyeth (Pfizer) also markets a derivative by the tradename TORISEL (temsirolimus) for the treatment of advanced renal cell carcinoma, which is administered intravenously. Temsirolimus is a water-soluble prodrug of sirolimus. Cordis, a division of Johnson & Johnson, markets a sirolimus-eluting coronary stent under the tradename CYPHER. In this context, the antiproliferative effects of sirolimus prevent restenosis in coronary arteries following balloon angioplasty. US 2010/0305150 to Berg et al. (Novartis) describes rapamycin derivatives for treating and preventing neurocutaneous disorders, such as those mediated by TSC including tuberous sclerosis, as well as those mediated by neurofibromatosis type 1 (NF-1). Rapamycin and its derivatives are further described in Nishimura, T. et al. (2001) Am. J. Respir. Crit. Care Med. 163:498-502 and in U.S. Pat. Nos. 6,384,046 and 6,258,823.
Rapamycin use in its clinically approved context has several known adverse effects including lung toxicity (the RAPAMUNE label warns that it is not indicated for lung transplant patients), increased cancer risk, and diabetes-like symptoms. Rapamycin is associated with the occurrence of pulmonary toxicity, usually in the form of interstitial pneumonitis, but pulmonary alveolar proteinosis has also been documented. See for example, Nocera et al., Sirolimus Therapy in Liver Transplant Patients: An Initial Experience at a Single Center, Transplantation Proceedings (2008), 40(6), 1950-1952; Perez et al., Interstitial Pneumonitis Associated With Sirolimus in Liver Transplantation: A Case Report, Transplantation Proceedings (2007), 39(10), 3498-3499; Hashemi-Sadraei et al., Sirolimus-associated diffuse alveolar hemorrhage in a renal transplant recipient on long-term anticoagulation, Clinical Nephrology (2007), 68(4), 238-244; Pedroso et al., Pulmonary alveolar proteinosis—a rare pulmonary toxicity of sirolimus, Transplant International (2007), 20(3), 291-296. The cause of rapamycin-induced pulmonary toxicity is not known.
Severe respiratory adverse events have also been associated with sirolimus use as an anti-cancer therapy under chronic administration resulting in circulating blood concentrations greater than 1 nanogram/mL range. For example, the lung toxicity of the sirolimus prodrug, temsirolimus, was documented in a 2009 report noting that “interstitial lung disease is a rare side effect of temsirolimus treatment in renal cancer patients”. Aparicio et al., Clinical & Translational Oncology (2009), 11(8), 499-510; Vahid et al., Pulmonary complications of novel antineoplastic agents for solid tumors, Chest (2008) 133:528-538. In addition, a 2012 meta-analysis concluded that 10% of cancer patients administered temsirolimus or everolimus may experience mild grade toxicity with a worsening of quality of life and, in some case, interruption of therapy. See Iacovelli et al., Incidence and risk of pulmonary toxicity in patients treated with mTOR inhibitors for malignancy. A meta-analysis of published trials, Acta oncologica (2012), 51(7), 873-879. Furthermore, safety pharmacology studies performed in rats with temsirolimus showed reductions in respiratory rate as well as alveolar macrophage infiltration and inflammation in the lungs (see Pharmacology Review for temsirolimus NDA 22088 available from the US FDA website). These adverse effects were observed under conditions of relatively high concentrations of the drug in the circulating blood volume as a result of systemic administration.
Despite its potential for toxicity to the lung, orally administered rapamycin has shown preliminary promise as a potential LAM therapy. See New Eng. J. Medicine 364:1595-1606 (2011) and review by Hammes and Krymskaya, Horn. Cancer 4(2):70-7 (2013); see also Ando et al. Respir Investig. 51(3):175-8 (2013) “The efficacy and safety of low-dose sirolimus for treatment of lymphangioleiomyomatosis”. But the clinical evidence also indicates the limitations of rapamycin in this context and the need for improved therapies and therapeutic regimens for the treatment of LAM. The primary limitations of rapamycin are the need to use the drug chronically, and most importantly, that rapamycin is associated with other adverse events (in addition to potential lung toxicities). For example, in a 24 month non-randomized open label trial completed in 20 patients, sirolimus administered orally was tested for its ability to reduce angiomyolipomas, which are slow growing hamartomas that can lead to renal failure in patients with TSC or sporadic LAM. Bissler et al. (2008) Sirolimus for angiomyolipoma in tuberous sclerosis complex or lymphangioleiomyomatosis. N Engl J Med 358(2):140-151. In that study, angiomyolipomas regressed “somewhat” during the treatment period but tended to increase after therapy stopped. Serious adverse events associated with sirolimus included diarrhea, pneumonia, pyelonephritis, cellulitis (from an animal bite), stomatitis, and hemorrhage of a renal angiomyolipoma. Dosing was based on the serum target levels that would prevent rejection in renal transplant patients and ranged from 1 to 15 ng/ml (blood sirolimus level). In another similar study (phase 2, non-randomized open label trial) 16 patients with TSC or sporadic LAM were treated with oral sirolimus for up to 2 years. Davies et al (2011) Sirolimus therapy for angiomyolipoma in tuberous sclerosis and sporadic lymphangioleiomyomatosis: a phase 2 trial. Clin Cancer Res 17(12):4071-4081. In that study, steady state blood levels of sirolimus were 3-10 ng/ml with more than half of the patients maintained on maintenance levels of 3-6 ng/ml. Sirolimus treatment showed sustained regression of renal angiomyolipomas. However, while tumor response was maintained with continuation of therapy, little further shrinkage occurred during the second year of treatment. Adverse events associated with sirolimus included oral mucositis, respiratory infections, and proteinuria. In another study of 10 LAM patients with documented progression, sirolimus was discontinued in 3 patients because of serious recurrent lower respiratory tract infection or sirolimus-induced pneumonitis. Neurohr et al., Is sirolimus a therapeutic option for patients with progressive pulmonary lymphangioleiomyomatosis? Respiratory Research (2011), 12:66. That study concluded that “sirolimus might be considered as a therapeutic option in rapidly declining LAM patients” but noted that its “administration may be associated with severe respiratory adverse events requiring treatment cessation in some patients” and that “discontinuation of sirolimus is mandatory prior to lung transplantation.” Finally, a 12 month randomized, double-blind 89 patient clinical trial was conducted with 46 patients having LAM, followed by a 12 month observation period. McCormack et al (2011) Efficacy and safety of sirolimus in lymphangioleiomyomatosis. N Engl J Med 364:1595-1606. Patients were maintained at sirolimus blood levels of 5-15 ng/ml. In this study, sirolimus treatment stabilized lung function, reduced serum VEGF-D levels, and was associated with a reduction in symptoms and improved quality of life. But stabilization of lung function required continuous treatment. Importantly, all of these clinical studies utilized oral formulations of sirolimus. This is because an aerosol formulation of rapamycin for delivery directly to the lungs was considered highly unlikely to succeed in view of rapamycin's well-known lung toxicity, as exemplified by the articles cited above.
A U.S. patent application by Lehrer published in 2013 reflects the view that “[r]apamycin (sirolimus) cannot be safely inhaled because of its well-documented lung toxicity, interstitial pneumonitis”. See US 20130004436, citing Chhajed et al. (2006) 73:367-374. The Lehrer patent application is directed to compositions and methods for treating and preventing lung cancer and lymphangioleiomyomatosis. Although some earlier publications, such as U.S. Pat. No. 5,080,899 to Sturm et al. (filed February 1991) and U.S. Pat. No. 5,635,161 (filed June 1995), contain some generic description of rapamycin formulated for delivery by inhalation, such generic descriptions were unsupported by any evidence and came before the many reported incidences of rapamycin-induced lung toxicity that appeared following its more widespread adoption as an immunosuppressant in the transplantation context and as an inhibitor of cellular proliferation in the anti-cancer context, as evidenced by the reports discussed above.
WO 2011/163600 describes an aerosol formulation of tacrolimus, which like rapamycin is a macrolide lactone. But tacrolimus is a distinct chemical entity from sirolimus and the molecular target of tacrolimus is calcineurin, not mTOR, and unlike rapamycin, tacrolimus did not show lung toxicity and in fact is indicated for preventing rejection following lung transplantations.
In view of the wide-spread recognition of the potential for rapamycin-induced lung toxicity, a pharmaceutical composition comprising rapamycin for pulmonary delivery in the treatment of LAM was not considered to be a viable therapeutic option in humans.
Delivery of drugs to the lung by way of inhalation is an important means of treating a variety of conditions, including such common local conditions as cystic fibrosis, pneumonia, bronchial asthma and chronic obstructive pulmonary disease, some systemic conditions, including hormone replacement, pain management, immune deficiency, erythropoiesis, diabetes, lung cancer, etc. See review by Yi et al. J. Aerosol Med. Pulm. Drug Deliv. 23:181-7 (2010). Agents indicated for treatment of lung cancer by inhalation include cisplatin, carboplatin, taxanes, and anthracyclines. See e.g., U.S. Pat. Nos. 6,419,900; 6,419,901; 6,451,784; 6,793,912; and U.S. Patent Application Publication Nos. US 2003/0059375 and US 2004/0039047. In addition, doxorubicin and temozolomide administered by inhalation have been suggested for treating lung metastases. See e.g., U.S. Pat. No. 7,288,243 and U.S. Patent Application Publication No. 2008/0008662.